The present invention pertains to a housing for electronic circuits and, more particularly, to an improved housing with a unitary die-cast for electronic circuitry designed to operate at very high frequencies.
There has been a long-felt need for a unitary die-cast with a minimum number of parts to house various operative functional parts of electronic circuitry, such as two-way radios with desirable electrical, acoustical and microphonic characteristics. Substantial research and development efforts have been made in recent years to design a single unitary die-cast with separate compartments for housing microphonically sensitive circuits, power supply or transmitter which generates considerable heat, and other functional parts, all to be contained in a single unitary die-cast assembly.
Significant advances have been made in recent years in the design of such a unitary die-cast housing assembly, as shown, for example, in the U.S. Pat. No. 4,091,232 to Gerd Garry Lenk and Robert Allen Paul, and assigned to Motorola, Inc., the assignee of the present invention. The patent shows a die-cast housing assembly, especially adapted to provide a low microphonic enclosure for certain type of circuits such as ceramic-based circuits which are very sensitive to acoustic vibrations. Microphonics refer to variations in the electrical performance of a circuit, such as, a change in the frequency of oscillation of an oscillator circuit, as a result of mechanical stress or vibrations imparted to the sensitive components in the electrical circuit. This problem is especially acute at very high frequencies since any motion of a component in an RF field may frequency or phase modulate the RF circuit, thereby inducing spurious modulation. The patent shows a low microphonic assembly that includes a housing with a cavity for receiving and supporting an electrical circuit board therein. A rigid cover is forcibly affixed to enclose the housing cavity by a plurality of fastening elements, such as screws, tightening the cover at the periphery thereof to the periphery of the housing.
While the aforementioned type of low microphonic circuit is found satisfactory, nevertheless, it has been found that the steps involved in fastening a plurality of screws is time-consuming, and, also, it is found that the amount of force applied to the screws for fastening them against the cover is not easily controllable. This resulted in relatively un-uniform pressure being exerted by the screws against the cover on the rim of the housing cavity. This tended to cause a relative decrease in the acoustic and microphonic dampening of the cavity.
According to yet another aspect of the prior art, difficulties are encountered in insulating a heat sensitive component or functional unit of radio circuits or electronic circuits from others which are more sensitive to heat. Usually thermal stabilizing circuits, heat sinking or dissipating members are used to dissipate the heat generated by certain parts of the electronic circuit, such as power supplies or transmitting circuitry.